Study On The Performance Of Quasi-solid State Aqueous Zinc Ion Batteries Using Polyacrylamide-based Hydrogel Electrolytes And Three-dimensional Electrodes

Depending on the increasing demand for wearable electronic devices,commercial lithium-ion batteries are unable to meet the requirements of high safety and low cost due to the use of organic electrolytes.Among various novel energy-storage systems,aqueous solution containing Zn salt is employed as the substitute for organic electrolyte,which endows aqueous zinc-ion batteries（AZIBs）with low cost and high safety.However,complicated Zn-storage mechanism of electrode materials,electrode dissolution,dendrite growth,side reactions and anode passivation during charging and discharging,greatly hinder long-term cycling stability of AZIBs.The hydrogel electrolyte prepared using polyacrylamide（PAM）as an additive shows low cost,and not only stabilize platting/stripping process of Zn metal anode,but also endows AZIBs with flexibility and self-healing.In this thesis,a series of PAM-based hydrogel electrolytes and several electrode materials were developed to be aimed at the challenges in design and preparation of electrode materials and electrodes of flexible AZIBs.Diversified tests were conducted to study the flexibility,self-healing and electrochemical performance of these hydrogel electrolytes.Meanwhile,Zn-storage mechanism of the cathode/anode materials were also studied.The quasi-solid state AZIBs were assembled with hydrogel electrolyte and different electrode materials.The flexibility and self-healing performance of the pouch cells were systematically studied.The research works carried out mainly include:（1）The studies were carried out to address the issues of poor conductivity and irreversible dissolution of cathode materials.Carbon cloth（CC）is employed as conductive substrate for the growth of VO₂@polyannile（PANI）nanobelt,enhancing the cathode high reversibility and flexibility.In addition,acrylamide（AM）monomer was in-situ polymerized in Zn Cl₂ aqueous solution under ultraviolet irradiation to form hydrogel electrolyte（called as PZC）.Owing to the suppression of active water molecules by polyacrylamide（PAM）framework,PZC hydrogel electrolyte presents an enlarged electrochemically stable window of 3.51 V,effectively avoiding side reactions.The Zn||Zn symmetric cell using PZC hydrogel electrolyte delivers stable lifespan exceeding 800 h at a current density of 1.0 m A cm^-2,while the Zn||Cu asymmetric cell presents high Coulombic efficiency of platting/stripping more than 99%,which is attributed to the suppression of dendrite formation in PZC hydrogel electrolyte.As for anode,Zn/CC prepared by electrochemically deposited Zn on the surface of CC shows great flexibility and self-standing.A quasi-solid state AIZB assembled by using VO₂@PANI/CC,Zn/CC and PZC hydrogel as flexible cathode,anode and electrolyte delivers the capacity maintenance of 221.5 m Ah g^-1 after 200 cycles at 0.2 A g^-1,it also shows an excellent rate-performance.Moreover,benefit from the hydrogen bond networks formed between water molecules with amino and carbonyl groups on the PAM framework,the quasi-solid state AZIB with PZC hydrogel electrolyte exhibit excellent cycling stability when suffered from bending and cutting/healing,laying the foundation for subsequent studies.（2）Except for surface modification,doping engineering for the preparation of vanadate is regarded as a facile and highly efficient strategy to eliminate the deficiencies of vanadium oxides.A flexible self-healing cathode was prepared by hydrothermal growth of Fe VO₄ nanoneedles grown on the surface of CC（FVO/CC）to achieve long-term cycling stability.Despite high concentration of Zn Cl₂ liquid electrolyte limits the activity of free water,the high density makes the hydrogel electrolyte occupying high mass ratio of total battery,which is unfavorable for the improvement of the energy density.Therefore,1.0 M Zn（CH₃COO）₂+0.1 M Mn（CH₃COO）₂ was employed as the substrate where AM monomer was polymerized by UV-initiated to obtain PAM-N,N’-methylenebisacrylamide（MBA）-Zn/Mn hydrogel electrolyte.The effect on the mechanical properties of the three-dimensional（3D）network structure constructed by MBA as crosslinker was also investigated.The PAM-MBA-Zn/Mn hydrogel electrolyte formed by crosslinking exhibited a wide electrochemically stable window and high ionic conductivity.The Zn||Zn asymmetric cell with PAM-MBA-Zn/Mn hydrogel electrolyte shows an overpotential of 40 m V after stably cycled for 250 h at a current density of 0.5 m A cm^-2,which was lower than that of the PAM-Zn/Mn and liquid electrolyte.The PAM-MBA-Zn/Mn hydrogel electrolyte brought a stable platting/stripping process for the zinc metal anode,which effectively suppressed dendrite growth.The quasi-solid-state AZIB assembled with FVO/CC cathode,electrodeposition Zn/CC anode,and PAM-MBA-Zn/Mn hydrogel electrolyte was tested by the galvanostatic intermittent titration technique（GITT）.It shows a low internal reaction resistance and fast Zn²⁺ion diffusion coefficients,implying enhanced rate-performance and long lifespan at high current density when PAM-MBA-Zn/Mn hydrogel electrolyte is used as electrolyte.Meanwhile,the quasi-solid state AZIBs exhibit excellent flexibility.The battery that was bent at 60°,90°,and180°for 30 times also show excellent cyclic stability compared to the batteries with no bending.The quasi-solid state AZIB achieves self-healing even cutting into 10 pieces and spliced together,showing a high voltage retention of 93.7%compared to the battery before cutting.The battery shows a high recovery then stabilized when suffers 3 times of cutting/healing in continuous cycling process.In addition,the flexibility of the battery enables it to be used as a strap to supply energy for electronic watch,showing potential application in flexible electronic devices.（3）In addition,a Prussian blue analogue（PBA）nanoparticle cathode(K_3.24Co₃[（CN）₆]₂·2H₂O,called as Co HCF NPs)with dual redox centers was designed and prepared to address the issue of relatively low capacity in AZIB,showing high theoretical capacity and working voltage（1.9 V）.The mechanical properties of hydrogel electrolyte can be improved by constructing dual-crosslinked polymer network,exhibit higher strength when suffered from stress deformation.Therefore,poly（vinyl alcohol）（PVA）was used as additive in PAM to form hydrogel electrolyte（called as PVM）which shows a dual-crosslinked structure.The dual-crosslinked structure brings higher mechanical strength to PVM hydrogel electrolyte,enabling it to be stretched more than 1490%.Benefit from the formation of hydrogen bonds between the amino,carbonyl and hydroxyl groups on the dual-crosslinked network and water molecules,PVM hydrogel electrolyte exhibits excellent flexibility and self-healing properties.The hydrogel can also be stretched up to 710%after 2 times of cutting-healing.In addition,the dual-crosslinked network endows the hydrogel electrolyte with an electrochemically stable window of 3.37 V,avoiding side reactions during charging and discharging.Zn||Zn symmetric cells using PVM hydrogel electrolyte shows a stable lifespan exceeding 500 h at the current density of 1.0 m A cm^-2,while showing a platting/stripping Coulombic efficiency more than 99%in Zn||Cu asymmetric cells.Moreover,operando observation of deposition behavior in Zn||Zn symmetric cells at a high current density of 75 m A cm^-2 further validated the inhibition of dendrite growth by PVM hydrogel electrolyte.The quasi-solid-state AZIBs assembled by using Co HCF NPs/CC,Zn/CC and PVM hydrogel as flexible cathode,anode and electrolyte,respectively,exhibiting excellent flexibility and self-healing performance.The batteries after different angles of bending show high capacity retention during galvanostatic charging-discharging tests.Compared with the first cycles,the batteries after cutting into 2,3 and 4 pieces then healing deliver the capacity retention of 119.1,108.6 and103.0 m Ah g^-1 after 30 cycles,respectively.The excellent flexibility and self-healing performance make the battery promising to be the candidate of next-generation energy storage system for wearable electronic devices.（4）Zn metal was employed as the anode for the quasi-solid-state AZIBs in the previous chapters,which need to eliminate dendrite growth,self-corrosion and surface passivation caused by self-corrosion and side reactions.Here,H₂Ti₅O₁₁·x H₂O（HTO·x H₂O）was grown on the surface of CC fibers via a hydrothermal method with cation exchange strategy,which is regarded as the substitute for Zn metal anode,demonstrating excellent cycling stability and rate performance at various current densities.A hydrogel（called as PMZ）electrolytewith high mechanical strength and self-healing properties was prepared by photoinitiated polymerization of AM monomers in 1.0 M Zn（CF₃SO₃）₂ liquid electrolyte.The PAM framework expands the electrochemically stable window for the PMZ hydrogel electrolyte,and the Zn||Zn symmetric cell assembled with the PMZ hydrogel electrolyte is stably cycled for more than 2000 h at 0.1 m A cm^-2,and the average Coulombic efficiency of the Zn||Cu asymmetric cell within 600 cycles is 98.94%,demonstrating the excellent performance of PMZ hydrogel electrolyte in stabilizing Zn metal anode.The quasi-solid state zinc ion"rocking chair"battery was assembled with Zn Mn₂O₄/CC,HTO·x H₂O/CC and PMZ hydrogel as flexible cathode,anode and electrolyte,respectively,showing excellent flexibility and self-healing performance.compared with the capacity before bending,the battery was bent four times during the continuous cycling process,showing high capacity recovery rate of 96.8%,94.9%,99.6%and 97.8%for each bending session,respectively.Four pieces of the cells cutting into 1,2,3 and 4 times then self-healing,showing the high-capacity retention of 62.9%,45.4%,25.7%and30.5%after 40 times of cycling.Therefore,the zinc-ion full batteries constructed by intercalated anode materials and hydrogel electrolyte shows potential applications in bendable flexible electronic devices.